The present invention relates to method of reducing the droplet size in aerosol spray devices which use a compressed gas propellant, and to an apparatus therefor.
An aerosol spray device incorporating a liquefied propellant, such as liquid butane produces an aerosol in which the liquid droplets are of relatively small size. For example, various known products which are produced as an aerosol spray using a liquefied propellant such as liquid butane (typically at 40 psi) having a diameter in the range of from 10 to 60 micrometers, with a peak distribution at around 30 to 40 micrometers. In comparison, if the liquid butane in such products is replaced by compressed gas at a pressure of 130 psi, the diameter range of the liquid droplets in the resultant aerosol spray is generally in the range of from 30 to 110 micrometers, with a peak distribution in the range of from 70 to 90 micrometers.
In aerosol spray devices which contain a liquefied propellant, such as butane the activation of the aerosol device causes the butane to evaporate instantly. As a result there are two mechanisms for the breaking up of the liquid while it is being expelled from the aerosol device. The first mechanism is the application of mechanical forces which act on the liquid as it is forced out of the body of the aerosol spray device through the spray head and into the atmosphere. The second mechanism is the evaporation of the liquid propellant, which itself causes or assists in the break-up of the liquid. The net effect is that the spray emerging from such an aerosol device contains liquid droplets of a relatively small size, as discussed above.
In contrast aerosol spray devices which use compressed air as the propellant rely entirely on the mechanical forces acting upon the liquid as it is sprayed from the aerosol device in order to break it up into droplets. Accordingly, the droplets are of relatively large diameter as compared to the size of the droplets from an aerosol spray device with a liquid propellant.
The relatively large droplet sizes produced by aerosol spray devices using a compressed gas propellant means that these aerosol spray devices are not suitable for some applications and aerosol spray devices incorporated liquefied propellants must be used. This is because the large droplet sizes produced by such aerosol spray devices are too wet and give a relatively poor dispersion of the product being sprayed.
We have now developed a method of reducing the droplet size of droplets sprayed from aerosol spray devices using a compressed gas propellant.